diff --git a/sys/dev/drm/radeon/r600_dma.c b/sys/dev/drm/radeon/r600_dma.c
--- a/sys/dev/drm/radeon/r600_dma.c
+++ b/sys/dev/drm/radeon/r600_dma.c
@@ -454,7 +454,7 @@
 
 	radeon_sync_create(&sync);
 
-	size_in_dw = (num_gpu_pages << RADEON_GPU_PAGE_SHIFT) / 4;
+	size_in_dw = ((u64)num_gpu_pages << RADEON_GPU_PAGE_SHIFT) / 4;
 	num_loops = DIV_ROUND_UP(size_in_dw, 0xFFFE);
 	r = radeon_ring_lock(rdev, ring, num_loops * 4 + 8);
 	if (r) {